Apparatus and method of manufacturing optical waveguides

ABSTRACT

An apparatus and method of manufacturing optical waveguides that comprises non-optically measuring the average temperature of a moving optical waveguide fiber as it exits a heated draw furnace using a temperature device. The device comprises an enclosed chamber that has a plurality of differential thermopiles secured to the inside surface, and a cooling system that substantially maintains a reference surface temperature of one end of each of the thermopiles. Each of the thermopiles are serially interconnected, whereby, in response to a maximum amount of radiant energy absorbed, the thermopiles generate an output signal. The output signal is substantially proportional to the maximum amount of radiant energy absorbed by the thermopiles, which in turn is substantially proportional to the fourth power of the average temperature of the moving optical waveguide fiber within the chamber.

[0001] This application claims priority to and the benefit of U.S.patent application Ser. No. 09/489,557 filed Jan. 21, 2000.

FIELD OF THE INVENTION

[0002] The invention relates to an apparatus and method of manufacturingoptical waveguides which comprises non-optically measuring the averagetemperature of a moving optical waveguide as it exits a heated drawfurnace that is heated to a draw temperature. In particular, theapparatus comprises a chamber having a plurality of differentialthermopiles to generate an output signal that is representative of amaximum amount of radiant energy radiated by the optical waveguide fiberwithin the chamber. While the invention may be used in manufacturingother types of optical waveguides, it is especially suited for use inmanufacturing silica optical waveguides, and will be particularlydescribed in that connection.

BACKGROUND OF THE INVENTION

[0003] An optical waveguide fiber is manufactured by drawing the opticalwaveguide fiber vertically from a heated optical waveguide preformlocated within a draw furnace. Because the moving optical waveguidefiber being drawn is at a high temperature of about 1500° C. to 1800°C., and due to the small diameter (about 125 microns) of the opticalwaveguide fiber, non-contact temperature measurement is a preferredchoice with such a small, moving or inaccessible optical waveguide. Onenon-contact way of measuring the temperature of an optical waveguidefiber is the use of radiation thermometers.

[0004] Temperature measurement with a radiation thermometer is based onthe fact that all objects emit radiant energy. Radiant energy is emittedin the form of electromagnetic waves, considered to be a stream ofphotons traveling at the speed of light. The wavelengths of radiantenergy emitted by a hot object range from the ultraviolet, 0.1 micron tothe far infrared, 100 microns. However, the majority of the energyradiated by an object between 1500° C. and 1800° C. is in the nearinfrared region, 1.0 to 2.0 microns. Radiation thermometers measure thetemperature of an object, such as an optical waveguide, by measuring theamount of thermal electromagnetic radiation received from a spot on theobject whose temperature is being measured. The intensity andwavelengths of the radiation emitted by an object depends on theemissivity and the temperature of the object. Emissivity is a measure ofan object's ability to emit radiant energy. The emissivity of an objectis the ratio of energy emitted while at a particular temperature to thatof a perfect emitter or “blackbody” at the same temperature. Sinceemittance will differ from one object to another, a standard, called ablackbody, is used as a reference for calibrating radiation thermometersand serves as the basis for the laws that define the relationship of theintensity of radiation and wavelength with temperature. A blackbody isan object having a surface that does not reflect or pass radiation. Itis considered a perfect emitter because it absorbs all electromagneticradiation to which it is exposed and re-emits the maximum spectralradiation allowed by Plank's law. The intensity of radiant energyincreases as temperature increases. Thus, such devices are capable ofmeasuring the temperature by measuring the intensity of the radiationthat the object emits.

[0005] A radiation thermometer consists of optical lenses that collectand focus the radiant energy emitted by an object, and a radiationdetector/sensor converts the focused radiant energy into an electricalsignal and an indicator provides a readout of the measurement. Adisadvantage of radiation thermometers is that they require a priorknowledge of the optical properties of the object being measured and,more specifically, the emissivity, ε of the object. Thermal radiation byan object always contains stray radiation emitted by the environmentsurrounding the object area and reflected by the object's surface.Hence, to maintain high measurement accuracy of a radiation thermometerprecise compensation/adjustment is necessary. For example, a radiationthermometer that is sensitive to energy in the wavelength range from 4.9μm to 5.5 μm with a spot size or field of view of 1.1 mm does not yieldaccurate temperature data when attempting to measure the temperature ofa 0.125 mm diameter optical fiber for several reasons. First, theaccuracy of a radiation thermometer is a function of the emissivity ofthe fiber within the sensitive wavelength range of the radiationthermometer, namely, 4.9 μm to 5.5 μm. Emissivity is the ratio of theemitted radiation by an object at specific wavelengths and temperatureto the emitted radiation from a blackbody at the same wavelengths andtemperature and unfortunately emissivity can be temperature and geometrydependent. The object, in this case is an optical waveguide fiber, whichis made primarily of silica. Silica is partially transparent toradiation at wavelengths shorter than approximately 8 microns forcertain thicknesses. Also, the effect of the cylindrical geometry of thefiber on its emissivity is not well understood. The above mentionedemissivity uncertainties along with the fact that the fiber occupiesapproximately only 15% of the thermometer's field of view as well asvibrating in and out of the field of view make any attempt to measureit's temperature using a radiation thermometer unreliable. One versionof a radiation thermometer attempts to overcome the vibrating fiberissue by using a panning mirror that pans an area looking for theoptical waveguide fiber and recording the peak temperatures over time.Thus, when the temperature peaks, it is assumed that the opticalwaveguide fiber is occupying the maximum 15% of the field of viewhowever the effective emissivity of the fiber is not known and thereforecannot be entered into the thermometer. Another disadvantage ofradiation thermometers is that they are quite expensive.

[0006] In light of the foregoing, it is desirable to provide anapparatus and method of accurately measuring the temperature of a movingoptical waveguide. In addition, it is desirable to provide an apparatusand method that minimizes any stray radiation and/or ambient temperaturechanges from effecting the temperature measurement of the opticalwaveguide. Further, it is desirable to provide an apparatus that isrugged and capable of withstanding high temperatures, as well as anapparatus that can consistently provide an accurate average temperaturemeasurement and has a fast response time. A further object of theinvention is to provide a reliable method of manufacturing silica glassoptical waveguides, while reliably monitoring and controlling thetemperature of the waveguide during the manufacturing process. Finally,it is desirable to provide an apparatus that is relatively inexpensiveto manufacture.

SUMMARY OF THE INVENTION

[0007] Accordingly, the present invention is directed to an apparatusand method of manufacturing optical waveguides that comprisesnon-optically measuring the average temperature of a moving opticalwaveguide fiber as it exits a heated draw furnace using a temperaturedevice or monitor. In particular, the invention provides an apparatusand method of measuring an average temperature of a moving opticalwaveguide, where the radiant energy emitted by the moving opticalwaveguide is non-optically processed by the temperature device. Theinvention provides an optical waveguide temperature monitor and a methodof measuring the average temperature of a moving optical waveguide bynon-optically detecting the radiant energy emitted by the moving opticalwaveguide and non-optically measuring the heat flux radiated by themoving optical waveguide within a chamber that is adapted to receive themoving optical waveguide through a central channel. The principaladvantage of the present invention is the provision of an arrangementthat overcomes the limitations and disadvantages of the described priorarrangements. Additional features and advantages of the invention willbe set forth in the description that follows, and in part will beapparent from the description, or may be learned by practice of theinvention. The objectives and other advantages of the invention will berealized and attained by the apparatus particularly pointed out in thewritten description and claims hereof as well as the appended drawings.

[0008] In accordance with one embodiment, the present invention is atemperature device or monitor used for manufacturing an opticalwaveguide. The temperature device comprises a thermally isolated chamberhaving a plurality of side walls and a central channel that traversesthe chamber from a top wall to a bottom wall, where the chamber isadapted to receive through the central channel the optical waveguidefiber being drawn. The device further comprises a plurality of heat fluxsensors, which in a preferred embodiment are differential thermopilesthat are secured to the inner surface of the side walls of the chamber.A first surface of each of the heat flux sensors that faces the centralchannel has a dark absorptive surface, which is exposed to the thermalenergy radiated by the optical waveguide fiber, whereas, a secondsurface of each of the heat flux sensors is thermally isolated from thefirst surface and is in thermal contact with the side walls of thechamber. The temperature monitor further comprises a cooling system thatis in thermal contact with the side walls, preferably, built into theside walls of the chamber. The cooling system is adapted tosubstantially maintain the reference surface temperature T_(s) of theside walls of the chamber. Thus, since the second surface of each of theheat flux sensors is in thermal contact with the side walls, the secondsurface is substantially maintained at the reference surface temperatureof T_(s) by the cooling system. As such, a temperature gradient developsbetween the first and second surfaces of the heat flux sensors and thistemperature gradient is translated into an output/voltage signal that isproportional to the thermal/radiant energy absorbed or the heat fluxmeasured by all of the heat flux sensors. Based on the amount of heatflux absorbed by the heat flux sensors, the average temperature of theoptical waveguide fiber can be determined. Also, each of the heat fluxsensors is serially interconnected to generate an aggregate outputsignal that is substantially proportional to a maximum amount of radiantenergy absorbed by all of the heat flux sensors within the chamber.Further, each of the heat flux sensors has an electrode that isconnected to a measuring device or readout instrument that registers anaggregate output signal generated by all the heat flux sensors. Theoutput signal is proportional to the thermal/radiant energy absorbed byeach of the heat flux sensors. In a preferred embodiment, the measuringdevice is a voltmeter.

[0009] In another embodiment, the invention provides an opticalwaveguide fiber manufacturing device. The manufacturing device comprisesof a draw furnace heated to a draw temperature, and an optical waveguidepreform positioned within the draw furnace, where the optical waveguidepreform is heated to the draw temperature. The manufacturing devicefurther comprises a temperature monitor for non-contact and non-opticalmeasurement of an average temperature T_(f) of an optical waveguidefiber being drawn from the heated optical waveguide preform. Thetemperature monitor is in alignment with and downstream from the drawfurnace. The temperature monitor (see comprises a thermally isolatedchamber having a plurality of side walls and a central channel thattraverses the chamber from a top wall to a bottom wall, where thechamber is adapted to receive through the central channel the opticalwaveguide fiber being drawn from the optical waveguide preform. Thechamber has a plurality of heat flux sensors, with each of the heat fluxsensors being mounted onto an inner surface of each of the side walls ofthe chamber. Preferably, each of the heat flux sensors is seriallyinterconnected to generate an aggregate output signal that issubstantially proportional to a maximum amount of radiant energyabsorbed by all of the heat flux sensors within the chamber. Theaggregate output signal is preferably substantially proportional to theaverage optical waveguide fiber temperature T_(f) of a length of theoptical waveguide fiber within the chamber. Further, the maximum amountof radiant energy absorbed from the optical waveguide fiber within thechamber is substantially proportional to the fourth power of the averagetemperature T_(f) of the length of the optical waveguide fiber withinthe chamber. The temperature monitor further includes a cooling systemthat is in thermal contact with each of the side walls of the chamber.The cooling system is adapted to substantially maintain a referencesurface temperature T_(s) of each of the side walls of the chamber.

[0010] In another aspect, the invention provides a method ofmanufacturing an optical waveguide fiber, where the method comprises thesteps of providing an optical waveguide preform, and heating the opticalwaveguide preform to a draw temperature, and then drawing an opticalwaveguide fiber from the heated optical waveguide preform. The methodfurther includes providing a heat flux chamber having an opticalwaveguide fiber entrance and an optical waveguide fiber exit, andpassing the drawn optical waveguide fiber through the entrance and outthe exit of the chamber. Finally the method includes the step ofnon-optically measuring the heat flux radiated by the optical waveguidefiber within the chamber. Preferably, the step of non-opticallymeasuring includes the steps of serially interconnecting an array ofheat flux sensors to an inner surface of a plurality of side walls ofthe heat flux chamber, and providing a cooling system that is in thermalcontact with the plurality of side walls of the heat flux chamber, wherethe cooling system is adapted to substantially maintain a referencesurface temperature of each of the heat flux sensors. The method furthercomprises adjusting the draw temperature based on a measured heat fluxof the of optical waveguide fiber within the chamber, where the measuredheat flux is proportional to the fourth power of an average temperatureof a length of the optical waveguide fiber within the chamber.

[0011] In yet another embodiment, the invention provides a method ofmeasuring an average temperature T_(f) of an optical waveguide fiberthat is being drawn from a heated optical waveguide preform in a drawfurnace. The method comprises the step of providing a chamber having aplurality of side walls and a central channel that traverses the chamberfrom a top wall to a bottom wall. The method also includes the steps ofserially interconnecting a plurality of differential thermocouple pairsonto a substrate to form a differential thermopile, and securely fixingeach of the differential thermopiles to an inner surface of each of theside walls of the chamber. Further, the method includes seriallyinterconnecting each of the differential thermopiles to a readoutinstrument that indicates the aggregate output signal generated by thedifferential thermopiles, the aggregate output signal beingrepresentative of the maximum amount of radiant energy absorbed by thedifferential thermopiles within the chamber. The method includes thestep of passing the optical waveguide fiber being drawn through acentral channel in the chamber. The method further includes the steps ofmaintaining a reference surface temperature T_(s) of one surface in eachof a plurality of differential thermopiles, where each of thedifferential thermopiles is fixed to an inner surface of the sidechamber with the one surface of each of the differential thermopilesbeing in thermal contact with the side walls of the chamber. The methodfurther includes generating an aggregate output signal representative ofa maximum amount of radiant energy absorbed by the differentialthermopiles within the chamber. The method further includes, providing acooling system that is in thermal contact with the side walls of thechamber, where the cooling system is adapted to substantially maintain areference surface temperature T_(s) of the one surface of thedifferential thermopiles. The method also includes providing within theside walls of the chamber a plurality of channels that are adapted toreceive a coolant from an external chiller that maintains the coolant atthe temperature T_(s). Also, in a preferred embodiment, the methodincludes a first thermocouple of each of the differential thermocouplepairs from a second thermocouple, with the first thermocouple beingexposed to the radiant energy radiating from the optical waveguide fiberand with the second thermocouple being in thermal contact with the innersurface of the side walls of the chamber. In a preferred embodiment, themethod includes providing a chamber that is made of aluminum.

[0012] It is to be understood that both the foregoing generaldescription and the following detailed description are exemplary andexplanatory and are intended to provide further explanation of theinvention as claimed.

[0013] The accompanying drawings are included to provide a furtherunderstanding of the invention and are incorporated in and constitute apart of this specification, illustrating embodiments of the invention,and together with the description serve to explain the objects,advantages, and principles of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

[0014]FIG. 1 is a perspective view showing an optical waveguidetemperature monitor in accordance with the present invention.

[0015]FIG. 2 is a perspective view of the optical waveguide temperaturemonitor of FIG. 1 showing the interior of the device.

[0016]FIG. 3A is a partial plan view showing the cooling system inone-half of the top wall of the apparatus shown in FIG. 2.

[0017]FIG. 3B is a partial plan view showing the cooling system inone-half of the bottom wall of the apparatus shown in FIG. 2.

[0018]FIG. 3C is a longitudinal plan view showing the cooling system inone-half of the device shown in FIG. 2.

[0019]FIG. 4 is a perspective view showing an arrangement of onedifferential thermocouple pair that is serially interconnected toproduce an output signal.

[0020]FIG. 5 is a plan view of a heat flux sensor in accordance with anembodiment of the present invention.

[0021]FIG. 6 is a longitudinal cross-sectional view of an opticalwaveguide manufacturing apparatus in accordance with an embodiment ofthe present invention.

DESCRIPTION OF THE INVENTION

[0022] The invention disclosed herein generally embodies the provisionof an apparatus and method of manufacturing optical waveguides thatcomprises non-optically measuring the average temperature of a movingoptical waveguide fiber as it exits a heated draw furnace using atemperature device or monitor. In particular, the invention provides anapparatus and method of measuring an average temperature of a movingoptical waveguide, where the radiant energy emitted by the movingoptical waveguide is not directly optically processed by a device havingany optical components, such as lenses. Rather, the invention providesan optical waveguide temperature monitor and a method of measuring theaverage temperature of a moving optical waveguide by non-opticallydetecting the radiant energy emitted by the moving optical waveguide andnon-optically measuring the heat flux radiated by the moving opticalwaveguide within a chamber that is adapted to receive the moving opticalwaveguide through a central channel. Generally, heat flux is calculatedby the formula HF=σF (T_(f) ⁴−T_(s) ⁴), wherein σ is theStefan-Boltzmann constant, and F is the calculated view factor for theinternal walls to the fiber length enclosed by the walls having a heighth, a radius of r₁ for the central opening, and a radius of r₂ for theoptical fiber, wherein r₁>r₂. More specifically, the invention providesan optical waveguide temperature monitor for measuring the averagetemperature of a moving optical waveguide fiber that is drawn from anoptical waveguide preform. The optical waveguide is passed through thecentral channel from the top through the bottom of the chamber.Preferably, each of the side walls of the chamber has a plurality ofheat flux sensors/detectors fixed or mounted to the inside of thechamber, preferably, only to the side walls of the chamber. A heat fluxsensor absorbs the thermal/radiant energy radiated by an opticalwaveguide fiber and generates a voltage output signal that issubstantially proportional to the heat flux. More specifically, the heatflux sensors used in the invention are differential thermopiles that aresensitive to all wavelengths of energy, and in a preferred embodiment,surround the optical fiber so that a maximum amount of radiant energyfrom the optical waveguide can be detected and measured. Accordingly,the heat flux sensors absorb the maximum amount of energy radiated bythe optical waveguide, and generate an output signal, namely, a voltagesignal that is substantially proportional to the amount of heat flux orthermal/radiant energy absorbed by the heat flux sensors. In particular,the amount of heat flux radiated from a length of optical waveguidewithin the chamber is proportional to the temperature of a length of theoptical waveguide fiber to the fourth power. Also, since the amount ofheat flux absorbed by any surface is a function of the surfacetemperature, monitoring and controlling the surface temperature of theheat flux sensors is necessary. Accordingly, a first surface of the heatflux sensors that faces the central opening is exposed to thethermal/radiant energy radiated by the optical waveguide fiber, whereas,an opposite second surface of each of the heat flux sensors is inthermal contact with the side walls of the chamber. Further, the sidewalls of the chamber has a cooling system that is designed tosubstantially maintain a reference surface temperature of T_(s). Sincethe second surface of the heat flux sensors is in thermal contact withthe side walls, the second surface of the heat flux sensors is alsosubstantially maintained at the temperature of T_(s) by the coolingsystem. As such, a temperature gradient develops between the first andsecond surfaces of the heat flux sensors, that is, across the thicknessof each of the plurality of thermopiles and this temperature gradient istranslated into an output/voltage signal that is proportional to thethermal/radiant energy absorbed, that is, the heat flux measured by theheat flux sensors at the surface facing the central channel of each ofthe thermopiles. The output signal from a differential thermopile isconnected via electrodes/contacts to a readout instrument, preferably, avoltmeter, where the voltage is proportional to the temperatureobserved. Based on the amount of heat flux absorbed by the heat fluxsensors, the average temperature of the optical waveguide can bedetermined. Additionally, in a prolonged measurement period, the coolingsystem in the temperature monitor which substantially maintains areference temperature ensures repeated accuracy of the temperature ofthe moving optical waveguide.

[0023] Referring to the drawings, FIG. 1 shows a perspective view of anoptical waveguide fiber temperature monitor 100 for non-opticallymeasuring an average temperature T_(f) of an optical waveguide fiber216, whereas, FIG. 6 shows a cross-sectional view of an opticalwaveguide manufacturing apparatus 200 that incorporates the temperaturemonitor 100 for non-optically measuring the average temperature of anoptical waveguide fiber 216 being drawn from a heated optical waveguidepreform 214 in a draw furnace 212 that is heated to a draw temperatureof approximately 2000° C. Although the invention is described in termsof measuring the average temperature of an optical waveguide fiber,modifications will be apparent to one skilled in the art to measure thetemperature of other types of optical waveguides. As shown in FIGS. 1-6,the temperature monitor 100 comprises a thermally isolated chamber 110having a plurality of side walls 112 and a central channel 114 thattraverses the chamber 110 from a top wall 116 to a bottom wall 118,where the chamber 110 is adapted to receive through the central channel114 the optical waveguide fiber 216 being drawn. The device 100 furthercomprises a plurality of heat flux sensors 120, which in a preferredembodiment are differential thermopiles 120 (shown in FIGS. 2 and 5)that are secured to the inner surface of the side walls 112 of thechamber 110. A first surface of each of the heat flux sensors 120 thatfaces the central channel 114 has a dark absorptive surface 122, whichis exposed to the thermal energy radiated by the optical waveguide fiber216, whereas, a second surface of each of the heat flux sensors 120 isthermally isolated from the first surface and is in thermal contact withthe side walls 112 of the chamber 110. The temperature monitor 100further comprises a cooling system 130 that is in thermal contact withthe side walls 112, preferably, built into the side walls 112 of thechamber 110. The cooling system 130 is adapted to substantially maintainthe reference surface temperature T_(s) of the side walls 112 of thechamber 110. Thus, since the second surface of each of the heat fluxsensors 120 is in thermal contact with the side walls 112, the secondsurface is substantially maintained at the reference surface temperatureof T_(s) by the cooling system 130. As such, a temperature gradientdevelops between the first and second surfaces of the heat flux sensors120 and this temperature gradient is translated into an output/voltagesignal that is proportional to the thermal/radiant energy absorbed orthe heat flux measured by all of the heat flux sensors 120. Based on theamount of heat flux absorbed by the heat flux sensors 120, the averagetemperature of the optical waveguide fiber 216 can be determined. Also,each of the heat flux sensors 120 is serially interconnected to generatean aggregate output signal that is substantially proportional to amaximum amount of radiant energy absorbed by all of the heat fluxsensors 120 within the chamber 110. Further, each of the heat fluxsensors has an electrode 127 that is connected to a measuring device orreadout instrument 230 that registers an aggregate output signalgenerated by all the heat flux sensors 120. The output signal isproportional to the thermal/radiant energy absorbed by each of the heatflux sensors 120. In a preferred embodiment, the measuring device 230 isa voltmeter 230. However, in an alternate embodiment, the measuringdevice 230 is a readout instrumentation, preferably, a digital displayunit that indicates the heat flux measured by the heat flux sensors 120.Furthermore, preferably, each of the heat flux sensors 120 is firstconnected to a differential amplifier that amplifies the output signal,which is then measured by a voltmeter 230. Alternatively, each of theheat flux sensors 120 can be individually connected to a measuringdevice 230 that is connected to a computer system that can compute oradd the output signal generated by each of the heat flux sensors 120 andthat can display the measured heat flux.

[0024] In one embodiment, the cooling system 130 includes a network ofchannels 132 (see FIGS. 3A-3C) that are built into the side walls 112 ofthe chamber 110. In particular, the network of channels 132 are adaptedto receive a coolant, preferably, water from an external chiller (notshown in any of the drawings), which is attached to the temperaturemonitoring device 100 via a tap 134 (shown in FIG. 1). The coolant ischanneled through the interior region of the side walls 112, thus,substantially maintaining the reference surface temperature T_(s) ofeach of the side walls 112, as well as, substantially maintaining eachof the second surfaces of each of the heat flux sensors 120 at thereference surface temperature of T_(s). Also, in a preferred embodiment,the network of channels 132 comprises a plurality of flexible tubes thatare adapted to receive a coolant from the external chiller. The coolantreceived into the channels 132 is substantially maintained at thetemperature T_(s) by the external chiller.

[0025] Furthermore, turning to the make-up of the heat flux sensors 120,as shown in FIGS. 4 and 5, each of the heat flux sensors 120 is made upof a plurality of differential thermocouple pairs 124. Morespecifically, as shown in FIG. 4, a first thermocouple 124A of each ofthe differential thermocouple pairs 124 is thermally isolated from asecond thermocouple 124B, with the second thermocouple 124B being inthermal contact with the inner surface of the side walls 112 of thechamber 110. Further, as shown in FIGS. 1, 2, 4 and 5, the differentialthermopiles 120 are each serially interconnected to generate anaggregate output signal substantially representative of a maximum amountof radiant energy absorbed by all of the thermopiles 120 within thechamber 110. The aggregate output signal is substantially proportionalto the average optical waveguide fiber 216 temperature T_(f) of a lengthof the optical waveguide fiber 216 within the chamber 110. In oneembodiment, each of the side walls 112 of the chamber 110 comprises adifferential thermopile 120 made up of a serially interconnected arrayof at least 1000 thermocouple pairs 124, preferably, at leastapproximately 1600 thermocouple pairs 124. The differential thermopiles120 used in the invention are sold under the trademark EPISENSOR and arecommercially available from Vatell Corporation of Christiansburg, Va.However, the differential thermopiles 120 used in the invention differfrom the EPISENSOR thermopiles in that the differential thermopiles 120were modified to exclude an optional foil thermocouple that can beembedded in each of the differential thermopiles 120 and further, thedifferential thermopiles 120 were constructed such that each thermopile120 was approximately a two inch square shaped thermopile comprising ofapproximately 1600 thermocouple pairs 124. The details of theconstruction of the differential thermopiles is described in U.S. Pat.No. 5,990,412, issued on Nov. 23, 1999, the specification of which ishereby incorporated by reference. The differential thermopiles 120 areconstructed using thick film printed ink manufacturing methods. Multiplelayers of electrically conductive and dielectric inks aredeposited/printed uniformly on a thin and flat anodized aluminumsubstrate to produce a differential thermopile, as shown in FIG. 5.Accordingly, each of the thermocouple pairs 124 is separated by a thinlayer of thermal resistance material. The differential thermopile 120measures the temperature difference across the thin and flat aluminumsubstrate. The substrate is oriented normal to a direction of the heatflow and the temperature difference is proportional to the amount ofheat flux passing through the substrate. The thin film constructionmakes these differential thermopiles 120 more rugged and improves theirresponse time. The thermal conductance of the differential thermopilesis at least approximately 64 W/m°K. Further, the differentialthermopiles 120 have an adhesive backing on the surface that is incontact with the side walls 112 of the chamber 110. Preferably, theadhesive backing is uniform and free of bubbles, which ensures goodthermal contact with the side walls 112 of the chamber 110 and, hence,provides accurate measurements. Moreover, the differential thermopiles120 have a coating with a high emissivity on the surface that is exposedto the incident radiation. Preferably, the coating is a high temperatureblack paint having an emissivity of at least 0.94.

[0026] Further, in a preferred embodiment of the manufacturing device200, as shown in FIG. 6, the temperature monitor 100 is in alignmentwith and located downstream from the draw furnace 212. The temperaturemonitor 100 further comprises a draw furnace controller 220 (shown inFIG. 6) that has an input from the temperature monitor 100, which allowsthe controller 220 to maintain the draw temperature of the draw furnace212. In particular, the measured temperature T_(f) of the length ofoptical waveguide fiber 216 is used to control the draw temperature ofthe draw furnace 212. Also, in another embodiment, the manufacturingdevice 200 further comprises an optical waveguide fiber coatingapparatus 218 (shown in FIG. 6) that is in alignment with and downstreamfrom the temperature monitor 100.

[0027] Also, in a preferred embodiment, the chamber 110 has four sidewalls 112, with each of the differential thermopiles 120 being fixed toone of the four side walls 112, such that the first surface of each ofthe differential thermopiles 120, which is preferably a dark absorptivesurface 122 faces the central channel 114 of the chamber 110 and isexposed to the radiant energy radiated by the optical waveguide fiber216 within the chamber 110. Moreover, in a preferred embodiment, thechamber 110 is made of a metal having a high thermal conductivity,preferably, in the range of 30W/m.K to 400 W/m.K, more preferably, athermal conductivity in the range of 170W/m.K to 237W/m.K, and in thepreferred embodiment the chamber is made of aluminum. In a preferredembodiment, the temperature monitor 100 is approximately three inches inheight with walls that are approximately ½ inch thick. Moreover, theheat flux sensors or the differential thermopiles 120 mounted onto thechamber 110 are squares that are approximately two inches on each side.Further, the diameter of the optical waveguide fiber is approximately125 microns, whereas, the diameter of the central channel 114 isapproximately 0.5 centimeters. In a preferred embodiment, the opticalwaveguide is approximately an inch away from the center of each of theheat flux sensors 120, and is approximately 1.4 inches away from theedge of each of the heat flux sensors 120. Additionally, in a preferredembodiment, the temperature monitor 100 has a locking mechanism 102 thatopens and closes the chamber 110 for receiving the optical waveguidefiber 216 being drawn from the optical waveguide preform 214 within thecentral channel 114.

[0028] In another embodiment, the invention provides an opticalwaveguide fiber manufacturing device 200, shown in FIG. 6. Themanufacturing device 200 comprises of a draw furnace 212 heated to adraw temperature, and an optical waveguide preform 214 positioned withinthe draw furnace 212, where the optical waveguide preform 214 is heatedto the draw temperature. The manufacturing device 200 further comprisesa temperature monitor 100 for non-contact and non-optical measurement ofan average temperature T_(f) of an optical waveguide fiber 216 beingdrawn from the heated optical waveguide preform 214. The temperaturemonitor 100 is in alignment with and downstream from the draw furnace212. The temperature monitor 100 (see FIGS. 1-6) comprises a thermallyisolated chamber 110 having a plurality of side walls 112 and a centralchannel 114 that traverses the chamber 110 from a top wall 116 to abottom wall 118, where the chamber 110 is adapted to receive through thecentral channel 114 the optical waveguide fiber 216 being drawn from theoptical waveguide preform 214. The chamber 110 has a plurality of heatflux sensors 120, with each of the heat flux sensors 120 being mountedonto an inner surface of each of the side walls 112 of the chamber 110.Preferably, each of the heat flux sensors 120 is serially interconnectedto generate an aggregate output signal that is substantiallyproportional to a maximum amount of radiant energy absorbed by all ofthe heat flux sensors 120 within the chamber 110. The aggregate outputsignal is preferably substantially proportional to the average opticalwaveguide fiber 216 temperature T_(f) of a length of the opticalwaveguide fiber 216 within the chamber 110. Further, the maximum amountof radiant energy absorbed from the optical waveguide fiber 216 withinthe chamber 110 is substantially proportional to the fourth power of theaverage temperature T_(f) of the length of the optical waveguide fiber216 within the chamber 110. The temperature monitor 100 further includesa cooling system 130 that is in thermal contact with each of the sidewalls 112 of the chamber 110. The cooling system 130 is adapted tosubstantially maintain a reference surface temperature T_(s) of each ofthe side walls 112 of the chamber 110.

[0029] In a preferred embodiment, each of the heat flux sensors 120 inthe temperature monitor 100 is a differential thermopile 120 that ismade up of a plurality of differential thermocouple pairs 124. Also, ina preferred embodiment, the network of channels 132 comprises aplurality of flexible tubes that are adapted to receive a coolant,preferably, water from the external chiller. The coolant received intothe channels 132 is substantially maintained at the temperature T_(s) bythe external chiller. The construction of the temperature monitor 100 inthe optical waveguide fiber manufacturing device 200 is in accordance tothat described herein above.

[0030] Also, in a preferred embodiment, the chamber 110 has four sidewalls 112, with each of the differential thermopiles 120 being fixed toone of the four side walls 112, such that the first surface of each ofthe differential thermopiles 120, which is preferably a dark absorptivesurface 122 faces the central channel 114 of the chamber 110 and isexposed to the radiant energy radiated by the optical waveguide fiber216 within the chamber 110. In a preferred embodiment, each of the sidewalls 112 of the temperature monitor 100 comprises at least 1000differential thermocouple pairs 124, preferably, approximately 1600differential thermocouple pairs 124. Furthermore, in a preferredembodiment, the temperature monitor 100 further comprises a lockingmechanism 102 that opens and closes the chamber 110 for receiving theoptical waveguide fiber 216 being drawn from the optical waveguidepreform 214. Also, preferably, the optical waveguide fiber manufacturingdevice 200 further comprises a draw furnace controller 220 formaintaining the draw temperature of the draw furnace 212, where the drawfurnace controller 220 includes an input from the temperature monitor100, as shown in FIG. 6. Thus, the measured temperature T_(f) of theoptical waveguide fiber 216 is used to control the draw temperature ofthe draw furnace 212. In addition, optical waveguide fiber manufacturingdevice 200 further comprises an optical waveguide fiber coatingapparatus 218 that is in alignment with and downstream from both thedraw furnace 212 and the temperature monitor 100, respectively. In yetanother embodiment, the optical manufacturing device 200 furthercomprises a second temperature monitor 100 that is in alignment with anddownstream from the optical waveguide fiber coating apparatus 218.

[0031] In another aspect, the invention provides a method ofmanufacturing an optical waveguide fiber 216, where the method comprisesthe steps of providing an optical waveguide preform 214, and heating theoptical waveguide preform 214 to a draw temperature, and then drawing anoptical waveguide fiber 216 from the heated optical waveguide preform214. The method further includes providing a heat flux chamber 110having an optical waveguide fiber entrance 113 and an optical waveguidefiber exit 115, and passing the drawn optical waveguide fiber 216through the entrance 113 and out the exit 115 of the chamber 110.Finally the method includes the step of non-optically measuring the heatflux radiated by the optical waveguide fiber 216 within the chamber 110.Preferably, the step of non-optically measuring includes the steps ofserially interconnecting an array of heat flux sensors 120 to an innersurface of a plurality of side walls of the heat flux chamber 110, andproviding a cooling system 130 that is in thermal contact with theplurality of side walls 112 of the heat flux chamber 110, where thecooling system 130 is adapted to substantially maintain a referencesurface temperature of each of the heat flux sensors 120. The methodfurther comprises adjusting the draw temperature based on a measuredheat flux of the of optical waveguide fiber 216 within the chamber 110,where the measured heat flux is proportional to the fourth power of anaverage temperature of a length of the optical waveguide fiber 216within the chamber 110.

[0032] In yet another embodiment, the invention provides a method ofmeasuring an average temperature T_(f) of an optical waveguide fiber 216that is being drawn from a heated optical waveguide preform 214 in adraw furnace 212. The method comprises the step of providing a chamber110 having a plurality of side walls 112 and a central channel 114 thattraverses the chamber 110 from a top wall 116 to a bottom wall 118. Themethod also includes the steps of serially interconnecting a pluralityof differential thermocouple pairs 124 onto a substrate to form adifferential thermopile 120, and securely fixing each of thedifferential thermopiles 120 to an inner surface of each of the sidewalls 112 of the chamber 110. Further, the method includes seriallyinterconnecting each of the differential thermopiles 120 to a readoutinstrument that indicates the aggregate output signal generated by thedifferential thermopiles 120, the aggregate output signal beingrepresentative of the maximum amount of radiant energy absorbed by thedifferential thermopiles within the chamber. The method includes thestep of passing the optical waveguide fiber 216 being drawn through acentral channel in the chamber 110. The method further includes thesteps of maintaining a reference surface temperature T_(s) of onesurface 124B in each of a plurality of differential thermopiles 120,where each of the differential thermopiles 120 is fixed to an innersurface of the side chamber 110 with the one surface 124B of each of thedifferential thermopiles being in thermal contact with the side walls112 of the chamber 110. The method further includes generating anaggregate output signal representative of a maximum amount of radiantenergy absorbed by the differential thermopiles 120 within the chamber110. The method further includes, providing a cooling system 130 that isin thermal contact with the side walls 112 of the chamber 110, where thecooling system 130 is adapted to substantially maintain a referencesurface temperature T_(s) of the one surface 124B of the differentialthermopiles 120. The method also includes providing within the sidewalls 112 of the chamber 110 a plurality of channels 132 that areadapted to receive a coolant from an external chiller that maintains thecoolant at the temperature T_(s). Also, in a preferred embodiment, themethod includes a first thermocouple 124A of each of the differentialthermocouple pairs 124 from a second thermocouple 124B, with the firstthermocouple 124A being exposed to the radiant energy radiating from theoptical waveguide fiber and with the second thermocouple 124B being inthermal contact with the inner surface of the side walls 112 of thechamber 110. In a preferred embodiment, the method includes providing achamber 110 that is made of aluminum.

[0033] Although a preferred embodiment of this invention and certainvariations thereof have been described herein, various modifications andvariations will be apparent to those skilled in the art withoutdeparting from the spirit or scope of the invention. Thus, it isintended that the present invention cover the modifications andvariations of this invention provided they come within the scope of theappended claims and their equivalents.

What is claimed is:
 1. A method of measuring the temperature T_(f) of an optical waveguide fiber being drawn from a heated optical waveguide preform in a draw furnace, said method comprising the steps of: passing said optical waveguide fiber through a chamber, said chamber being positioned downstream from said draw furnace; maintaining a reference surface temperature T_(s) of one surface of each of a plurality of differential thermopiles, each of said differential thermopiles being fixed to an inner surface of said chamber; and generating an aggregate output signal representative of the radiant energy absorbed by said differential thermopiles within said chamber.
 2. The method of claim 1, wherein said passing step includes: providing said chamber having a plurality of side walls and a central channel that traverses said chamber from a top wall to a bottom wall.
 3. The method of claim 2, further comprising the steps of: serially interconnecting a plurality of differential thermocouple pairs to form one of said plurality of differential thermopiles; and securing said one of said plurality of differential thermopiles to an inner surface of each of said side walls of said chamber.
 4. The method of claim 3, wherein a first thermocouple of each of said differential thermocouple pairs is thermally isolated from a second thermocouple, said second thermocouple being in thermal contact with said side walls of said chamber.
 5. The method of claim 3, further comprising the step of: serially interconnecting each of said differential thermopiles in said chamber to a voltmeter.
 6. The method of claim 5, further comprising the step of: providing a cooling system that is in thermal contact with said side walls of said chamber, said cooling system being adapted to substantially maintain a reference surface temperature T_(s) of each of said second thermocouples of said differential thermopiles.
 7. The method of claim 6, wherein said providing step includes: providing within said side walls of said chamber a plurality of channels that are adapted to receive a coolant having an approximate temperature T_(s).
 8. The method of claim 7, wherein said amount of radiant energy absorbed by said differential thermopiles is substantially proportional to the fourth power of the average optical waveguide fiber temperature T_(f) of a length of optical waveguide fiber within said chamber.
 9. The method of claim 8, wherein said chamber is made of aluminum.
 10. A method of manufacturing an optical waveguide fiber, said method comprising the steps of: providing an optical waveguide preform; heating said optical waveguide preform to a draw temperature; drawing an optical waveguide fiber from said heated optical waveguide preform; providing a heat flux chamber having an optical waveguide fiber entrance and an optical waveguide fiber exit; passing said drawn optical waveguide fiber through said entrance and out said exit; and non-optically measuring the heat flux radiated by said optical waveguide fiber within said chamber.
 11. The method of claim 10, wherein said non-optically measuring step includes: serially interconnecting an array of heat flux sensors to an inner surface of a plurality of side walls of said heat flux chamber; and providing a cooling system that is in thermal contact with said plurality of side walls of said heat flux chamber and is adapted to substantially maintain a reference surface temperature of each of said heat flux sensors.
 12. The method of claim 10, further comprising adjusting said draw temperature based on a measured heat flux of said length of optical waveguide fiber within said chamber.
 13. The method of claim 12, wherein said measured heat flux is proportional to the fourth power of an average temperature of said length of optical waveguide fiber within said chamber.
 14. An optical waveguide temperature device for non-optically measuring an average temperature T_(f) of a length of optical waveguide fiber being drawn from a heated optical waveguide preform in a draw furnace heated to a draw temperature, said device comprising: a thermally isolated chamber having a plurality of side walls and a central channel that traverses said chamber from a top wall to a bottom wall, said chamber being adapted to receive through said central channel said length of optical waveguide fiber being drawn; a plurality of differential thermopiles secured to the inside surface of said side walls of said chamber, a first surface of each of said differential thermopiles being thermally isolated from a second surface, said first surface of each of said differential thermopiles faces said central channel and has a dark absorptive surface, said first surface of each of said differential thermopiles being exposed to said heat flux, said second surface being in thermal contact with said side walls of said chamber, said second surface of said differential thermopiles having a reference surface temperature of about T_(s); and a cooling system in thermal contact with said side walls of said chamber, said cooling system being adapted to substantially maintain said reference surface temperature T_(s) of said side walls of said chamber.
 15. The temperature device of claim 14, wherein said cooling system includes a network of channels built into said side walls of said chamber, said network of channels being adapted to receive a coolant from an external chiller that substantially maintains said reference surface temperature T_(s) of each of said differential thermopiles.
 16. The temperature device of claim 14, wherein each of said differential thermopiles includes a plurality of differential thermocouple pairs, a first thermocouple of each of said differential thermocouple pairs being thermally isolated from a second thermocouple and in thermal contact with said side walls of said chamber, said second thermocouple having a reference surface temperature of about T_(s).
 17. The temperature device of claim 14, wherein each of said differential thermopiles generates an output signal that is substantially proportional to an amount of radiant energy absorbed from said length of optical waveguide fiber within said chamber.
 18. The temperature device of claim 14, further comprising a draw furnace controller for maintaining said draw temperature of said draw furnace.
 19. The temperature device of claim 14, wherein said draw furnace is in alignment with and upstream from said chamber.
 20. The temperature device of claim 19, wherein said temperature T_(f) of said length of optical waveguide fiber is used to control said draw temperature of said draw furnace.
 21. The temperature device of claim 20, wherein a maximum amount of radiant energy absorbed by said differential thermopiles is substantially proportional to the fourth power of said average optical waveguide fiber temperature T_(f) of said length of optical waveguide fiber within said chamber.
 22. The temperature device of claim 21, wherein said chamber is made of a metal having a thermal conductivity in the range of 170 W/m.K to 237 W/m.K.
 23. The temperature device of claim 22, wherein each of said side walls of said chamber comprises a serially interconnected array of at least 1000 thermocouple pairs.
 24. The temperature device of claim 23, wherein each of said side walls of said chamber comprises a serially interconnected array of approximately 1600 thermocouple pairs.
 25. The temperature device of claim 24, wherein said network of channels comprises a plurality of flexible tubes that are adapted for connection to said external chiller.
 26. The temperature device of claim 25, wherein said coolant received into said channels is substantially maintained at said temperature T_(s) by said external chiller.
 27. The temperature device of claim 26, further comprising an optical waveguide fiber coating apparatus in alignment with and downstream from said chamber.
 28. The temperature device of claim 27, wherein each of said differential thermopiles is serially interconnected to an output signal measuring device.
 29. The temperature device of claim 28, wherein said metal is aluminum.
 30. An optical waveguide fiber manufacturing device, said device comprising: a draw furnace heated to a draw temperature; an optical waveguide preform positioned within said draw furnace, said optical waveguide preform being heated to said draw temperature; a temperature monitor for non-contact measurement of an average temperature T_(f) of an optical waveguide fiber being drawn from said heated optical waveguide preform, said temperature monitor being in alignment with said draw furnace and including: a thermally isolated chamber having a plurality of side walls and a central channel that traverses said chamber from a top wall to a bottom wall, said chamber being positioned downstream from said draw furnace, said chamber being adapted to receive through said central channel said optical waveguide fiber being drawn from said optical waveguide preform, said chamber having: a plurality of heat flux sensors adapted to measure an amount of heat flux radiated by said optical waveguide fiber within said chamber, each of said heat flux sensors being fixed securely to an inner surface of said side walls of said chamber; and a cooling system in thermal contact with said side walls of said chamber, said cooling system being adapted to substantially maintain a reference surface temperature T_(s) of each of said heat flux sensors.
 31. The device of claim 30, further comprising a draw furnace controller for maintaining said draw temperature, said draw furnace controller including an input from said temperature monitor.
 32. The device of claim 30, wherein said temperature T_(f) of said optical waveguide fiber is used to control said draw temperature of said draw furnace.
 33. The device of claim 30, wherein each of said heat flux sensors comprises a plurality of differential thermocouple pairs, wherein said amount of heat flux radiated by said optical waveguide fiber within said chamber causes a temperature gradient to develop across each of said differential thermocouple pairs.
 34. The device of claim 30, wherein a first thermocouple of each of said differential thermocouple pairs is thermally isolated from a second thermocouple, said second thermocouple being in thermal contact with said inner surface of said side walls of said chamber.
 35. The device of claim 30, wherein said cooling system comprises a plurality of flexible channels, each of said channels being adapted to receive a coolant whose temperature is substantially maintained at said reference surface temperature T_(s) by an external chiller.
 36. The device of claim 35, wherein said second thermocouple of each of said differential thermocouple pairs is in thermal contact with at least one of said channels, and wherein said coolant received through said channels substantially maintains said reference surface temperature T_(s) of each of said second thermocouples.
 37. The device of claim 36, wherein each of said differential thermocouple pairs is serially interconnected to form a differential thermopile.
 38. The device of claim 37, wherein said chamber has four side walls, said differential thermopile being fixed to each of said side walls, wherein a surface of each of said differential thermopiles facing said central channel of said chamber has a dark absorptive surface.
 39. The device of claim 38, wherein each of said side walls comprises at least 1000 differential thermocouple pairs.
 40. The device of claim 39, wherein said differential thermopiles are serially interconnected to generate an aggregate output signal representative of a maximum amount of radiant energy absorbed from said optical waveguide fiber within said chamber.
 41. The device of claim 40, wherein said aggregate signal is substantially proportional to said average optical waveguide fiber temperature T_(f) of said length of optical waveguide fiber within said chamber.
 42. The device of claim 41, wherein said maximum amount of radiant energy absorbed from said optical waveguide fiber within said chamber is substantially proportional to the fourth power of said average temperature T_(f) of said length of optical waveguide fiber within said chamber.
 43. The device of claim 42, wherein said chamber is made of a metal having a thermal conductivity in the range of 170 W/m.K to 237 W/m.K.
 44. The device of claim 43, further comprising a locking mechanism that opens and closes said chamber for receiving said optical waveguide fiber being drawn from said optical waveguide preform.
 45. The device of claim 44, further comprising an optical waveguide fiber coating apparatus in alignment with and downstream from each of said draw furnace and said temperature monitor.
 46. The device of claim 45, further comprising a second temperature monitor in alignment with and downstream from said temperature monitor. 